1. Field of the Invention
The present invention relates to a quantum device wherein quantum dots are arrayed in two-dimensional configuration. The quantum dots arrayed on the quantum device can be preferably used as a single-electron transistor, doping diode, doping transistor, doping transistor array and semiconductor light emitting device.
2. Description of Related Art
Devices that utilize single-electron tunnel effect such as single-electron transistors and single-electron memories are attracting much attention. The single-electron transistor, for example, is a promising candidate that can replace MOSFETs to satisfy the requirements of miniaturization of devices to the order of sub-micron for which improvements on the MOSFETs, the mainstream technology in the field of semiconductor transistors, are reaching limitations thereof.
A fine particle surrounded by thin insulation layer receives electrons from an external electrode by the tunnel effect. Because the particle has a capacitance C with respect to the outside, electrostatic energy of the particle changes by e2/2C when an electron enters therein. This prohibits subsequent electron from entering the fine particle by the tunnel effect. Therefore, in order to fabricate the device utilizing the single-electron tunnel effect, it is inevitable to arrange quantum dots on an insulator, the quantum dots being formed from microscopic metal particles having electrostatic energy higher than energy xcex94E (approximately 25 mV) required for thermal excitation of an electron at room temperature. In case e2/2C has a low value, it is inevitable to make an array of quantum dots having energy just above the Fermi level of a microscopic dot higher than the thermal excitation level of electron. Although single-electron operation is lost in this case, transistor operation can still be achieved. Also microscopic lead wires must be formed even when a quantum device can be achieved, because the tunnel effect does not occur with wide lead wires of conventional circuits due to parasitic capacitance accompanying the lead wires.
As a single-electron memory, a prototype device was made as a fine line (100 nm wide) of polycrystal Si film having an extremely small thickness of 3.4 nm and a gate electrode (100 nm) crossing each other via an oxide film gate of 150 nm by depositing a-Si in a depressurized CVD process and crystallizing it at 750xc2x0 C. (Japanese Journal of Applied Physics: Vol. 63, No. 12, pp. 1248, 1994). This device operates at a room temperature and has a potential for the use as an nonvolatile memory which operates at a speed exceeding the limitation of the conventional flash memory. Also an aluminum-based single-electron transistor having an island electrode measuring 20 nm was fabricated by means of electron beam lithography and triangular shadow evaporation technologies (Jpn. J. Appl. Phys., Vol. 35, 1996, pp. L1465-L1467). This single-electron transistor has advantages which are not found in silicon-based devices, for example, a periodical gate modulation characteristic wherein background current does not depend on the gate voltage.
However, the single-electron memory based on the polycrystal Si film is unstable because there are variations in the Si film thickness. Also the Al-based single-electron transistor operates at 100 K, far below the room temperature, and is not of practical use.
Thus, an object of the present invention is to provide a quantum device which operates stably at the normal temperature and is applicable for commercial production of single-electron transistors and single-electron memories.
Another object of the present invention is to provide extremely small devices such as diode, transistor and semiconductor light emitting devices doped with extremely small amounts of impurities, not experienced in the prior art, by utilizing microscopic dots arranged in the quantum device.
In order to achieve the above and other objects, the quantum device of the present invention is constituted from a two-dimensional array of quantum dots formed from metal atom aggregates contained in a metalloprotein complex arranged on the surface of a substrate having an insulation layer at least on the surface thereof with a pitch of the size of the metalloprotein complex.
The metal which constitutes the metal atom aggregates used in the quantum device is preferably one that can ionize in an aqueous solution. For example, the metal may be iron Fe, aluminum Al, phosphorus P, germanium Ge, zinc Zn, manganese Mn, arsenic As, gold Au, silver Ag, tungsten W or the like, while Fe is preferable.
The diameter of the metal atom aggregates used in the quantum device is 7 nm or smaller, preferably 5 nm or smaller, and the pitch of the metalloprotein complex is preferably from 11 to 14 nm.
In a method appropriate for manufacturing the quantum device of the present invention, first the metalloprotein complex is let to be absorbed onto a denatured protein membrane, polypeptide membrane or LB membrane developed on a surface of an aqueous solution. The membrane is then placed on a substrate which is durable to temperatures beyond a burn-out temperature of the protein and has an insulating property on the surface thereof, to burn out the protein component in a gas atmosphere which does not react with the substrate. The metalloprotein complex is turned into a metal oxide and remains on the substrate in a pattern of dots spaced by a pitch of the size of the protein molecule. Then the metal oxide is heated in a reducing atmosphere to be reduced. The metal oxide is thus reduced into metal atom aggregates which are arranged in a two-dimensional array on the substrate.
The metalloprotein complex used in the quantum device of the present invention is preferably ferritin, but the protein may also be one derived from phage or virus.
As the substrate used in the quantum device of the present invention, silicon substrate has wide applicability, but a glass substrate or a ceramic substrate may also be used.
A single-electron transistor of the present invention is constituted from quantum dots which are formed from metal atom aggregates contained in metalloprotein complex and arrayed in a two-dimensional configuration with a pitch of the size of the metalloprotein complex on the surface of a substrate which is durable to temperatures beyond the burn-out temperatures of the protein and has an insulation layer on the surface thereof, and comprises a quantum well made of a first quantum dot, an electrode section made from at least three quantum dots located around the quantum well and a wiring section which connects the quantum dots other than those around the quantum well and the electrode section, wherein the electrode section has a source and a drain comprising second quantum dots and third quantum dots, respectively, which oppose each other, and a control gate comprising fourth quantum dots that remain.
The metal used in the metal atom aggregates, the metalloprotein complex and the substrate of the single-electron transistor may be the same as those used in the quantum device described above.
The diameter of the metal atom aggregate used in the single-electron transistor is 7 nm or smaller, or preferably 5 nm or smaller, which means that one aggregate normally comprises several thousands of atoms, depending on the metal element. As a consequence, the transition level nearest to the Fermi level of the aggregate is higher than the thermal excitation level of electron at room temperature. The quantum well and the electrode section are separated by a distance of 11 to 14 nm which allows the tunnel effect to occur. Therefore, the tunnel effect can be observed in the single-electron transistor at the room temperature or at around the temperature of liquid nitrogen.
An appropriate method for manufacturing the quantum transistor of the present invention comprises, in addition to the steps of manufacturing the quantum device described above, a step of irradiating the metal atom aggregates with an electron beam of a scanning electron microscope, of which a beam width is set to be not greater than the pitch, in a vacuum in the presence of a trace of carbon compound, while scanning the electron beam to have carbon vapor-deposited between the metal atom aggregates thereby forming lead wires. This causes the source and the drain to be connected with the quantum dots other than those around the quantum well by carbon wires. The source of carbon supply may be residual gas consisting mainly of hydrocarbons coming from vacuum pump oil. This wiring method, which makes it possible to make extremely fine wires spaced by a distance of the order of nanometers, is best suited to the manufacturing of microscopic devices such as single-electron transistor.
A diode of the present invention has quantum dots formed from metal atom aggregates wherein donor impurities and acceptor impurities formed from metal atom aggregates contained in metalloprotein complex hetero-dimer are arrayed with a pitch of the size of the metalloprotein complex on the surface of a substrate having an insulation layer on the surface thereof, and has an n-type region, a p-type region and a pn junction formed by diffusing the donor impurities and the acceptor impurities via the insulation layer into the substrate, an electrode section formed in a specified configuration and a wiring section which connects the n-type region, the p-type region and the electrode section.
An appropriate method of fabricating the diode of the present invention comprises the step of arraying donor impurities and acceptor impurities with a pitch of the size of the metalloprotein complex on the surface of the substrate, comprising the steps of (a) fabricating a metalloprotein complex hetero-dimer which includes the donor impurities and the acceptor impurities formed from metal atom aggregates; (b) absorbing a metalloprotein complex hetero-dimer onto an LB membrane developed on the surface of an aqueous solution; (c) placing the LB membrane having the metalloprotein complex hetero-dimer absorbed thereon on a substrate which is durable to temperatures beyond the burn-out temperature of the protein and has an insulation layer on the surface thereof, and burning out the protein through heat treatment in an inert gas that does not react with the substrate; (d) reducing in a reducing atmosphere thereby to obtain metal atom aggregates; (e) forming the n-type region, the p-type region and the pn junction by diffusing the donor impurities and the acceptor impurities via the insulation layer into the substrate by heat treatment; (f) forming the electrode section by patterning electrodes of a specified configuration; and (g) irradiating the n-type region, the p-type region and the electrode section with an electron beam of a scanning electron microscope, of which beam width is set not to be greater than the pitch, in a vacuum in the presence of a trace of carbon compound, while scanning the electron beam to have carbon vapor-deposited between the n-type region and the electrode section, and between the p-type region and the electrode section, thereby forming lead wires.
A transistor of the present invention has quantum dots comprising metal atom aggregates and donor impurities or acceptor impurities formed from metal atom aggregates contained in metalloprotein complex hetero-trimer which are arrayed with a pitch of the size of the metalloprotein complex, while a group of impurities capable of forming a npn structure formed from acceptor impurities having donor impurities on both sides thereof or a group of impurities capable of forming a pnp structure formed from donor impurities having acceptor impurities on both sides thereof is arranged on the surface of the substrate, so that the n-type region, the p-type region and the pn junction formed by diffusing the donor impurities and the acceptor impurities via the insulation layer into the substrate, the electrode section formed in a specified configuration, and the wiring section connecting the n-type region, the p-type region and the electrode section are provided.
A manufacturing method appropriate for the transistor of the present invention comprises the step of arranging donor impurities and acceptor impurities on the surface of a substrate with a pitch of the size of the metalloprotein complex, comprising the steps of (a) fabricating metalloprotein complex hetero-trimer by holding the acceptor impurities or the donor impurities on both sides of the donor impurity and the acceptor impurity formed from metal atom aggregates; (b) absorbing a metalloprotein complex hetero-trimer onto an LB membrane developed on the surface of an aqueous solution; (c) placing the LB membrane having the metalloprotein complex hetero-trimer absorbed thereon on a substrate which is durable to temperatures beyond the bum-out temperature of the protein; (d) burning out the protein through heat treatment in an inert gas that does not react with the substrate; (e) reducing the metalloprotein complex in a reducing atmosphere; (f) forming the n-type region, the p-type region and the pn junction by diffusing the donor impurities and the acceptor impurities via the insulation layer into the substrate by heat treatment; (g) forming an electrode section of a specified configuration; and (h) irradiating the n-type region, the p-type region, the pn junction and the electrode section with electron beam of a scanning electron microscope, of which beam width is set to be not greater than the pitch, in a vacuum in the presence of a trace of carbon compound, while scanning the electron beam to have carbon vapor-deposited between the n-type region and the electrode section, and between the p-type region and the electrode section, thereby forming lead wires.
The metal used in the metal atom aggregates, the metalloprotein complex and the substrate of the diode and the transistor may be the same as those used in the quantum device described above, and the diameter of the metal atom aggregate is similarly 7 nm or smaller, or preferably 5 nm or smaller.
The manufacturing method appropriate for the diode and the transistor is different from the manufacturing method for the single-electron transistor, in that two or three kinds of metalloprotein complexes of different metal elements are combined and absorbed onto the substrate in the form of hetero-dimer or hetero-trimer, and that the donor impurities and the acceptor impurities are diffused by heating to a temperature from 1000 to 1200xc2x0 C.
The diode and the transistor thus obtained measure about 10 nm by 30 nm, and is expected to operate at an extremely high speed.
A transistor array of the present invention comprises transistors arranged in a two-dimensional array at intervals of an integer number times the pitch, which is from 11 to 14 nm, wherein quantum dots comprise metal atom aggregates contained in metalloprotein complex hetero-trimer having at least one layer of apoprotein in the surrounding thereof with donor impurities or acceptor impurities formed from metal atom aggregates being arranged with a pitch of the size of the metalloprotein complex, while a group of impurities capable of forming a npn structure formed from acceptor impurities having donor impurities on both sides thereof or a group of impurities capable of forming pnp structure formed from donor impurities having acceptor impurities on both sides thereof is arranged on the surface of the substrate, the transistor having an n-type region, a p-type region and a pn junction formed by diffusing the donor impurities and the acceptor impurities via an insulation layer into the substrate, an electrode section formed in a specified configuration and a wiring section for connecting the n-type region, the p-type region and the electrode section.
A manufacturing method appropriate for the transistor array of the present invention is basically similar to that of the method of manufacturing the transistor described above, although different in that the hetero-trimer is absorbed onto the substrate while being surrounded by a multitude of protein molecules which do not include metals, for example a multitude of apoferritin molecules. Both the protein comprising metalloprotein complex and the protein such as apoferritin are burned out. Finally, the acceptor impurities and the donor impurities are arranged at a pitch of the size of the protein, while a group of impurities and a group of other impurities originating from one hetero-trimer are arranged at intervals an integer n times the size of the protein which is from 11 to 14 nm. The integer n can be controlled in terms of the number of protein layers which surround the hetero-trimer.
Because the transistor array of the present invention has transistors arranged at intervals of the order of nanometers, around ten billion transistors per square centimeter can be packaged on a chip, making it possible to achieve an amplifier of high gain.
The manufacturing method appropriate for microscopic dots of the order of nanometers having quantum effects, comprises the steps of arranging quantum dots formed from a plurality of metal atom aggregates contained in a metalloprotein complex in two-dimensional configuration on a surface of a substrate having an insulation layer with a pitch of the size of the metalloprotein complex, and forming column shaped structures on the surface of the substrate by plasma etching via said masking quantum dots, and insulating a space between said column shaped structures.
A semiconductor light emitting device of the present invention has p-type and n-type semiconductor layers and an activation layer formed on an insulating substrate, wherein masking quantum dots formed from a plurality of metal atom aggregates contained in a metalloprotein complex are arranged in a two-dimensional array on the surface of the activation layer with a pitch of the size of the metalloprotein complex, and quantum dots formed from the activation layer are formed by plasma etching via the masking quantum dots.
A manufacturing method appropriate for the semiconductor light emitting device of the present invention is different from the method of manufacturing the quantum device described above only in that the quantum dots are arrayed on the surface of a light emitting layer laminated on the insulating substrate, while the step of forming the quantum dots from the activation layer by plasma etching is included with the arrayed quantum dots being used as the mask.
The metal contained in the metal atom aggregates, the metalloprotein complex and the substrate used in the semiconductor light emitting device may be the same as those used in the quantum device described above, and diameter of the metal atom aggregate is similarly 7 nm or smaller, or preferably 5 nm or smaller.